1. Field of the Invention
The present invention relates to a data processing apparatus and a card-sized data processing device. More particularly, the present invention relates to a data processing apparatus and a card-sized data processing device which execute prescribed tasks, extracting data and electric power from a received carrier wave that is modulated with an information signal.
2. Description of the Related Art
Card-sized data processing devices with contactless interface have become of interest in recent years, with growing expectations for their various applications, ranging from personal use (e.g., credit cards and commuter passes) to industrial use (e.g., electronic data tags for factory automation and warehouse management purposes). Such devices often provide processing functions to perform sophisticated tasks. To meet today's market needs, they have to have a microprocessor with a higher processing speed, inevitably resulting in increased power consumption. Some designers overcome this problem by optimizing the power supply system in a device, considering the operating voltage of each circuit block. More specifically, a lower supply voltage is provided to digital circuits that can operate at a relatively low voltage, while a higher supply voltage is fed to analog circuits that need a relatively high voltage to satisfy dynamic range requirements. By integrating two dedicated power supply circuits, the power consumption of card-sized data processing devices can be minimized.
FIG. 11 shows a typical structure of a conventional card-sized data processing device. As seen, the illustrated device is composed of the following elements: an antenna 10, four diodes 11-1 to 11-4, a supply voltage generator 13, a demodulator 14, a clock circuit 15, a reset circuit 16, a modulator 17, a microprocessor unit (MPU) 18, and a nonvolatile memory 19.
The antenna 10 emits and captures a radio wave to/from external card reader/writer equipment (not shown) which contains a carrier wave modulated with an information signal. The four diodes 11-1 to 11-4 form a bridge circuit, which full-wave rectifies the radio wave signal received by the antenna 10, thereby extracting the information signal and DC power.
From the DC power appearing at the junction point of the diodes 11-1 and 11-2, the supply voltage generator 13 produces a supply voltage #1 for analog circuits and a supply voltage #2 for digital circuits. More specifically, the supply voltage #1 is fed to the demodulator 14, clock circuit 15, reset circuit 16, and modulator 17, while the supply voltage #2 is fed to the MPU 18 and nonvolatile memory 19.
FIG. 12 shows the detailed structure of the supply voltage generator 13. As seen, the supply voltage generator 13 is composed of a regulator 20, a first capacitor 21, a level converter 22, and a second capacitor 23. With the electric power supplied through the diodes 11-1 and 11-2 (FIG. 11), the regulator 20 outputs a DC voltage with the level adjusted to the intended supply voltage #1. The first capacitor 21 reduces the output impedance of the regulator 20, besides eliminating ripple components contained in its output. The level converter 22 steps down the output of the regulator 20, from supply voltage #1 to supply voltage #2. The second capacitor 23 reduces the output impedance of the level converter 22, besides eliminating ripple components contained in its output.
Referring back to FIG. 11, the demodulator 14 reproduces an information signal from the bridge output signal (i.e., the signal appearing at the junction point of the diodes 11-1 and 11-2) and sends the result to the MPU 18. The clock circuit 15 extracts a clock signal from the bridge output signal and sends it to the MPU 18. The reset circuit 16 produces a reset signal from the bridge output signal and sends it to the MPU 18. The modulator 17 modulates a carrier wave with an output data signal supplied from the MPU 18.
The MPU 18 performs various computational operations according to firmware programs stored in the nonvolatile memory 19 and also to the incoming data signal supplied from the demodulator 14. The processing result is stored back into the nonvolatile memory 19 or supplied to the modulator 17 for transmission. The nonvolatile memory 19 is such a storage device that can retain the stored data even if the power supply is shut down. It stores programs and data that are necessary for the MPU 18 to execute its tasks.
As seen from the above explanation, the demodulator 14, clock circuit 15, reset circuit 16, and modulator 17 operate at a supply voltage #1, while the MPU 18 and nonvolatile memory 19 at another supply voltage #2 that is set to be lower than the supply voltage #1 so as to suppress their power consumption. The conventional device is configured in this way to improve its power requirements.
As a general trend, the operating voltage of microprocessors have been going down with each passing year, and some processors available today can even operate at 1.8 V, for example. In contrast, the supply voltage of nonvolatile memories stays at a relatively high level of about 3 V because such memory devices require a certain magnitude of energy to read or write data. This constraint about memory voltage leads to a problem with the conventional device explained in FIG. 11. That is, the circuit designer cannot reduce the supply voltage #2 further because the nonvolatile memory 19 does not allow it. In this sense, the nonvolatile memory 19 is a bottleneck in low-power design of such data processing devices.
Another problem in the conventional circuit of FIG. 11 is that the MPU 18 and nonvolatile memory 19 are powered up at the same time. The nonvolatile memory 19 requires steadiness of its supply and control signal voltages for correct operation. Simultaneous activation of the MPU 18 may cause an unintended behavior of the nonvolatile memory 19 during the power-up.